1. Field of the Invention
This invention relates in general to certain new and useful improvements in both an apparatus and a method for sharpening a cutting tool. More particularly, the invention relates to a device of the type for sharpening a cutting tool by shifting an abrasive element under the tool's cutting edge. The tool is adjustably clamped at a selected angle and with a uniform pressure between the tool and an abrasive element, while the abrasive element is shifted back and forth by the user. This invention enables a precise and accurate sharpening of the tool by an inexperienced user.
2. Brief Description of the Prior Art
Cutting tools, and particularly, those used in wood cutting machinery, such as routers, thickness planers and the like, frequently require sharpening or honing and, to some extent, may even require grinding. The same holds true of many hand-held cutting tools and particularly wood cutting tools, such as chisels and the like. The present state of the art usually resides in manually holding the cutting tool and bringing the same into contact with a rotating abrasive element, such as a grinding wheel, or otherwise, by manually moving the cutting tool against a fixed abrasive element such as a sharpening stone.
For the manufacturer of cutting tools, the sharpening of the tool is a relatively simple task, when the necessary and very costly machinery is available. However, for the users of these cutting tools who do not have the availability of this very expensive and highly technical sharpening machinery, the task of sharpening a tool to obtain a precise cutting edge becomes rather difficult. In order to obtain proper cutting with a tool, it is necessary to maintain a uniform cutting edge on the tool. Moreover, the uniformity of this edge is desirably duplicated on each occasion when the tool is sharpened. When a tool is hand-held and brought into contact with an abrasive element, or when the abrasive element is hand-held and brought into contact with the tool by some manual means, precision of the cutting angle and uniformity of the cutting edge is materially sacrificed.
Conventional bench grinding wheels which usually comprise an abrasive stone rotated by an electric motor arrangement have been used for sharpening. In this case, the tool is physically held into contact with the rotating abrasive stone. However, and here again, it can be seen that this is a very rudimentary and non-precise way of sharpening a tool.
There are devices which function in the nature of a guide for sharpening chisels and plane blades. In one case, a frame holds the chisel or plane blade in relation to a fixed abrasive stone. The frame is somewhat L-shaped and utilizes a roller at one end for riding on a table or other supporting surface while the chisel or plane blade is clamped to the other end of the frame and extends into contact with the abrasive stone. One of the ostensible purposes of this device is to achieve a precise angle of the cutting edge. However, when manually moving a tool in contact with an abrasive stone, there is nothing to preclude a rockable movement and there is no means to obtain a predetermined sharpening pressure which is uniform from edge to edge of the tool.
Another prior art device clamps a chisel or plane blade and is provided with a roller for riding directly on the surface of the abrasive stone and the cutting edge of the tool is brought into contact with the abrasive stone as the device is moved along the stone. However, there is no means to obtain a constant uniform pressure when the tool is moved by hand across and against an abrasive stone. Still another prior art device allows the change of a honing angle for microbevel sharpening without removing the tool from a guide. Nevertheless, there is also no means to maintain a uniform pressure when moving the tool by hand.
An experienced craftsman can sharpen a cutting tool quite accurately. Unfortunately, most people are not experienced craftsmen.
Holding a cutting tool and bringing the same into contact with an abrasive element, as shown in the prior art devices, is a very archaic and inaccurate way to grind, sharpen or hone a tool. Usually, the party holding the tool or the abrasive element or moving one relative to the other, cannot hold and move the tool or abrasive element with a uniformity of pressure and angle of attack in order to ensure that there is a linear cut which is uniform across the length of the cutting edge of the tool. Moreover, it is virtually impossible to obtain a constant and uniform pressure between the tool and the abrasive element by manually holding one or the other and this desired consistency and uniformity of sharpening is sacrificed.
It can be seen that there have been several apparatus which employ a stationary abrasive element and which allows the cutting tool to be brought into contact with and moved across the abrasive element. In all such cases, there is no inexpensive device which enables a cutting tool to have a cutting edge sharpened with precise uniformity and at a correct cutting angle across the cutting edge and with uniformity from one sharpening to the next. In addition, there has not been any low-cost device which enables the sharpening of a secondary or microbevel on the tip of a cutting tool with precise uniformity and angle.
There are no simple devices for sharpening tools such as router bits, shaper cutters and similar tools. The usual way of sharpening these tools is by holding the bit or tool by hand and moving it back and forth on a hone or otherwise, by moving the hone against the bit or tool. Further, there are no effective and low cost devices which allow for the sharpening of solid carbide and carbide-tipped cutting members.
There has been a need for an inexpensive and effective apparatus which allows an inexperienced user to sharpen a cutting tool reliably. However, this can be accomplished in accordance with the present invention by the user moving the abrasive stone back and forth under the cutting edge of the tool. When the tool is properly positioned in the apparatus, the apparatus will keep the angle and the amount of pressure between the cutting edge of the tool and the stone fixed thereby yielding correctly sharpened tools.